Plasticizing cellulosic structures



Patented Feb. 27, 1940 PATENT OFFICE 2,191,; ms'ncrzmo CltILULOSIG s'mno'ruans Frederick W -Meigs, Wilmington, M, as-

signer to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Dela- No Drawing. Application May 9, 1939, Serial No. 272,843

5 Claims. '(ci. 9168) This invention relates to cellulosic structures, especially those of pellicular nature. More particularly, it relates to a method for producing flexible and durable cellulosic pellicles by treating the same with softening agents, and the products resulting from such treatment. 1

In the manufacture of cellulosic pellicles-of the type precipitated from aqueous alkaline cellulosic solutions, such as regenerated'cellulose pellicles,

0 including sheets or films, caps, bands, continuoustubing, artificial straw and the like, it has long been customary to incorporate into the cellulosic pellicle a softening agent in order to maintain it in a flexible condition. Such cellulosic pellicles,

15 when free from a softening agent, are known to be quite brittle, and while a softener-free pellicle may find certain uses, a softened and therefore flexible sheet or film is much more generally useful. Heretofore, -as softeners forregenerated 2o cellulose, and similar water-sensitive cellulosic pellicles, the art has applied such substances as ethylene glycol, propylene glycol, diethylene glycol, formamide, glycerol, and the like, but of these,

by far the most important is glycerol which has hitherto known no equal as a softening agent of general utility for producing flexible, trans- ,parent, and durable water-sensitive cellulosic pellicles such as those of regenerated cellulose.

Many attempts have been made to find'a softener 5 for water-sensitive cellulosic pellicles which will be as cheap as and which will have the generally useful softening characteristics of glycerol. After a by-product from the soap industry. As a by-f product, the quantity may be limited and hence glycerol is subject to market fluctuations of supply as well as price. Glycerol has been particularly high-priced and diificultly obtainable during periods ofswar when large quantities are used in the production of munitions. The glycols,

mentioned above as useful cellulose softenera, are for the most part obtained by a relatively expensive process of The glycols are 50 also-relatively volatile and are therefore unsatisiacto for use in softening some types of cellulosic pellicles. For an industry consuming large am unts of these materials, therefore, the de- :ivelopment of' less expensive-equivalents or means gm reducing; the. :0 m v terials will mean a marked economy in production.

It is, therefore, an object of this invention to provide a new and useful method for producing softened-water-sensitive cellulosic materials possessing desirable physical properties. It is a further object of this invention to provide watersensitive cellulosic materials having a softening agent associated therewith, which softening agent will not interfere with any subsequent treatment of the cellulosic pellicles, such as the application of surface coatings, ink,'coloring matter, adhesives, or the like. It is a still further object of this invention to provide-a rigid, flexible, transparent, durable cellulosic pellicle, such as a sheet, film, or tube of regenerated cellulose in which the softening agent consists in whole or in part of a water-soluble ethanolamine salt of an alphahydroxy aliphatic acid. Other objects of the invention will appear hereinafter.

By the term "rigidity or its equivalent as used herein is meant that property which is the opposite of limpness: in other words; rigidity in the sense thatithe pellicle can be advanced in a wrapping machine or similar apparatus without curling, crumpling or otherwise fouling the machine.

The term durability is used to define resistance to shock or rough handling. Thus, for example, bags may be fabricated from the pellicle and filled with some standard material such as a certain weight of dried beans, and the package sealed, whereupon thedurability may be measured against a known standard by dropping the package under standard conditions and noting the re,-

'sistance oi the wrapper to breakage.

The objects of this invention can be attained,

in general, by treating a regenerated cellulose pellicle, or a like water-sensitive cellulosic'pellicle,

with a softening agent comprising a water-soluble ethanolamine salt of an alpha-hydroxy aliphatic acid containing 2 or 3 carbon atoms in the acid constituent. As specific examples of such compounds may be mentioned: monoethanolamine .glycollate, diethanolamine glycollate, triethanolamine glycollate, monoethanolamine lactate, diethanolamine lactate, and triethanolamine lactate. The excess softening agent is then removed from the pellicleand the pellicle so treated is In the manufacture of regenerated cellulose sheets or films, as ior example. by the viscose process. the celiulosic dispersion is formed into a sheet or film by passing the same through suit able apparatus into coagulating and/or regenerating baths from which it is finally obtained in the form of a continuous cellulosic sheet which is customarily led in a continuous manner through a series of purifying, bleaching and washing operations. Just prior to the drying operation which is also usually continuous, coordinating with the sheet forming and purification opera tions, the film is passed through a bath containing a softening agent in such concentration that after the excess liquid has been removed from the surface of the-sheet by suitable squeeze rolls and the excess moisture removed by passage through the dryer, the final sheet can be'wound up in a continuous fashion and will contain an appropriate predetermined amount of softening agent.

The commercially available dry regenerated cellulose film contains .approximately 4 to 8% moisture. Depending upon the particular uses for which the product is destined, the softening agent in the sheet. or film, usually glycerol, may vary from about 8 to 25%, based on the combined weight of the cellulose and softening agent in the sheet.

The total amount of softener in'the film is controlled primarily by the total amount of softening agent in the treating bath; film thickness, rate of passage through the bath, temperature of the bath, etc., may also contribute thereto to a certain extent. The regenerated cellulose pellicle, when reaching the treating bath, is in a highly swollen and hydrated condition and usually the cellulose of the pellicle is associated with 300% or more of water. This highly swollen sheet, is impregnated with the treating bath.

Because of the large amount of water associated with the cellulose, it is apparent that the removal of this water during the drying operation will concentrate the softening agent with respect to the cellulose content of the pelliclel Thus it is that if a regenerated cellulose pellicle containing about 15% total softener is desired as a final product, the concentration of softener in the treating bath will be adjusted to approximately one-third thatvalue, or about 5%. This is true when the softening agents are, like glycerol and the improved agents of this invention, substantially non-volatileand are not vaporized during the drying operation. -It is obvious that if a mixed softener is used, the components of which are appreciably volatile duringthe drying operation, then the softener concentration of the treating bath must be increased sufiiciently to compensate for the loss thereof during the drying step.

It has now been discovered that salts of the type indicated above are extremely well suited as softening agents for water-sensitive cellulosic pellicles, that is, pellicles produced from aqueous alkaline cellulosic solutions or dispersions coagulated in an acid coagulating bath, especially those of regenerated cellulose,,and that they may be used as substitutes for glycerol in this capacity.

Furthermore, pellicles of regenerated cellulose' Example I A sheet or film of gel regenerated cellulose, in

which the final dry thickness will be about .0009",-

is immersed in or drawn through an aqueous bath containing mono-ethanolamine glycollate in such" concentrations that the final dried product will contain about 6.3% moisture and 15% softener, based on the combined weight of cellulose and softener in the film. The sheet or film is allowed to remain in contact with the bath until thoroughly impregnated, whereupon it is removed from the bath. the excess liquid being drained off or removed by suitable squeeze rolls, blotters, on the like, when the film can be dried in the usual manner down to the final moisture content indicated above. When tested at a relative humidity of about 35% at 24 C., or even at relative humidities as low as 15% to 22% at ordinary temperatures,- the durability of the film is found to be at least equal to that of a similar regenerated cellulose film softened with about 14% glycerol.

Example II A sheet or continuous film of gel regenerated cellulose such that the final dry thickness will a final film containing about 6.3% moisture and 17-18% ethanolamine lactate. In the case, the

final product will be equal to or better than a similar regenerated cellulose sheet or film bearing 15% to 16% glycerol as softener, insofar as its physical properties are concerned, including transparency, flexibility and durability under varying conditions.

In a similar manner, the compositions of the: following examples are substituted for the bath of Example I, the remainder of the treatment being the same as in Example I.

Example III Per cent by weight Diethanolamine glycollate 6.0 Water 94.0

Example IV Per cent by weight Triethanolamine lactate 5.5 Water 94.

v Example V Per cent by weight Triethanolamine glycollate 5.5 Water 94.

- Example VI Per cent by weight Diethanolamine lactate 6.0 .Water --s f 94.0

Sheetsv or films of gel regenerated cellulose treated with any of the baths described in Examples III to V1, inclusive, in accordance with the procedure outlined in'Example I, will show physical characteristics I substantially equal to those of a similar regenerated cellulose sheet treated with a softener bath containing 5% of glycerol (that is, a final film containing about 15% glycerol), especially when the physical properties includes transparency flexibility, rigidity, durability, and the like. Moreover, films pro duced as indicated above will be found to have superior. surface-characteristics over those" ex hibited by films. which have been softened by glycerol. j I

The following two examples illustrate a method for softening regenerated cellulose film with glycerol in combination with a salt of the present invention.

Example VI! A sheet or continuous film of gel regenerated cellulose .simllarto that of Example I is treated in the manner described in Example I, using, however, a treating bathof the following approximate composition:

v Per cent by weight Glycerol 2.5

lthanolamine glycollate 2.5

Water Example VIII Similarly, the following bath composition is substituted for that of Example I:

. Per cent by weight Glycerol 2.5 Ethanolamine lactate 2.5 Water 95.0

softener is admixed with ethanolamine ,saitii of 'glycollic acid, when compensation is ma de'lgfor loss during the drying operation.

Example IX Asheet or continuous film of gel regenerated cellulose, such that the final dry thickness will be about .0009", is immersed in or passed through a treating bath of the following approximate I composition: a

v Per cent by weight Monoethanolamine glycollate 2.75 Ethylene glycol 2.75 Water 94.5

In this bath the ratio of monoethanolamine glycollate to ethylene glycol is about 'lzl. The

film is treated as described in Example I and yields a final product containing about 6.3% moisture, 8.25% monoethanolamine glycollate and 6.6% ethylene glycol. The ratio of monoethanolamine glycollate to ethylene glycol in the dried film is thus about 1.25:1.0, the amount-of ethylene glycol having beendecreased by loss during the drying operation. The dried film is subsequently provided with a surface coating which may be of any type' desired.

Thus, for example, it maybe provided with a moistureprooilngcoating whichmay conveniently contain a cellulose derivative, a plasticizer, a resin or blending agent and a moisturep'roofing agent'such as a wax or wax-like material; The surface coating in this case serves the double purpose of providing a moistureproof product-and of preventing loss by evaporation of the relatively volatile ethylene glycol. Even when tested under such drastic conditions as described in Example I, the product is transparent, flexible and more durable than a similar film softened with l% glycerol alone. c

It is obvious that in theabove examples the concentration of total softening agent in the' treating bath may be suitably varied according to the base being treated, in order. that the final product will have the appropriate amount of softener.

As a base. the invention contemplates the use 3 of any water-sensitive cellulosic -structure',,par- I ticularly of pellicular nature such as a sheet or film, artificial straw, caps, bands, or continuous, tubes, such as may be obtained by the coagulation and/or regeneration from an aqueous cellu-v' 5' losic dispersion in accordance withthe procedure customary to the art. Thus, the invention comprehends the use of, regenerated cellulose pellicles such as may be obtained from the viscose or cuprammonium processes, as well as pellicles l0 composed of glycol cellulose, cellulose glycollic acid, lowly esterifled orlowly etherified cellulose derivatives where there is only one other or ester group associated with several cellulose units, and other cellulosic structures of similar' character.

Similarly, various types of paper, especially of the glassine type, may be used as base materials. As a matter of convenience, the invention has been described in terms of its application to the 0- softening of regenerated cellulose pellicles such as these sheets or films of regenerated cellulose which are suitable for use as wrapping tissue, it being understood thatthe scope of the invention includes any of the other bases set forth above and that the invention is equally .applicable thereto.

All of the examples given have been set forth in terms of a sheetor film of gel regenerated cellulose (gel regenerated cellulose being de- 80. fined as a water-swollen regenerated cellulose Y which has never been dried-hence that product which is obtained from the -wet end'of the casting machine). Obviously, this is the more prac- --tical way of-practicing the invention, since the softening agent is customarily incorporated into the sheet or film while the latter is in the gel state and during the normal course of manufacture. Obviously, if one desires to impregnate an already dried regenerated .c llulose film with 40 a softenerof the character de cribed, it is possible to rewet the dried film so as to render it highly swollen, whereupon it may be treated with treating baths similar to those described, but of composition suitable for obtaining the final prodg I uct desired. In the same way, any-of the sheets set forth as equivalent to regenerated cellulose sheets can be substituted in the specific examples.

The invention has been described in part in m terms of the use of glycerol in combination with the softeners of the present invention. It is to be understood that other similar known cellulose softeners may besubstituted for the glycerol and among those may be mentioned ethylene glycol,

diethylene glycol, triethylene glycol, formamide, carbamide, and-other substances known to the art as softeners for water-sensitive cellulose structures.

It is also to be understood that various mix- 69 tures of the newly described softening agents 'may be employed with single softeners of the prior art or with mixtures ofthe latter, depending upon the type of final film desired and the purposes for which the film is to be used. T

If'a colored cellulosic pellicle is desired, it may be obtained in any of the wayscommonly knownin the art. including the passage of the sheet of the sheet or-film through a bath containing a suitabiedyestufi. If desired, the dyer stuff maybe added to the bath used fgr introducing the softening agent. In the same way, after. the film has been treated with the soften mt, it may be subjected to any of the ary after treatments such as seeing or coating, or the like, which may be customarily given to celiulosic pellicles of the type described, in just the same manner that a glycerol softened regenerated cellulose film, for example, may be treated.

The instant invention offers numerous advantages over the prior art means of softening cellulosic pellicles of the type described. Since the softening agents of the present invention are substantially solid substances at ordinary temperatures, the control of concentrations used for treating baths is greatly simplified. Because of their crystalline nature, the softening agents are available in highly purified condition and consequently improve, the quality of theflnal product. However, unlike many crystalline compounds, they do not crystallize after incorporation in the sheet in the concentrations useful for softening' They can be obtained syntheti-' cally at a very low cost in comparison to the cost of known softeners and they are available in unlimited quantity independent of a by-product j source. l

The use of the newly described softening agents results in a product having improved physical characteristicstics, particularly im' proved transparency, flexibility, durability and surface properties.

Furthermore, sheets or films of regenerated cellulose impregnated with the materials of this invention have been found excellent bases for coating compositions of a type suitable for moistureproofing the final product. Coating compositions well known to the art, and particularly those containing cellulose derivatives, are found to adhere tenaciously to base sheets of nature and spirit of the invention, it is to be understood that the invention is not to be limited thereto except as set forth in the following claims.

I claim:

1. A flexible, durable, water-sensitive cellulosic structure, said structure containing, as a softener therefor, a water-soluble ethanolamine salt of an alpha-hydroxy aliphatic acid containing 2 or 3 carbon atoms in the acid constituent.

2. A flexible, durable, regenerated cellulose structure, said structure containing, as a softenertherefor, a water soluble ethanolamlne salt of analpha-hydroxy aliphatic acid containing 2 or 3 carbon atoms in the acid constituent.

3. A flexible, durable, water-sensitive cellulosic structure, said structure containing, as a sof-- tener therefor, monoethanolamine glycollate.

4. A flexible, durable, water-sensitive cellulosic structure, said structure containing, as a softener therefor, diethanolamine glycollate.

6. A flexible, durable, water-sensitive cellulosic structure, said structure containing, as a softener therefor, monoethanolamine lactate.

FREDERICK MADISON MEIGS. 

